In contrast to the ozone depleting solvents such as CFCs, and halogenated solvents, water immiscible petroleum, synthetic and/or natural terpene hydrocarbons or hydrocarbons modified with other additives or surfactants are increasingly used as alternative sources for the cleaning of metallic and non-metallic surfaces. However, these solvents are always accompanied with rinsing and drying problems. Briefly, solvents are difficult to be rinsed off the surfaces with plain water and consequently require prolonged drying times and relatively high temperatures. Drying off these solvents is associated with potential fire or environmental hazards, particularly those with low flash point solvents. Similar problems have also been found for surfaces cleaned with other water immiscible non-halogenated solvent cleaners including medium-high molecular weight alcohols, ethers, amines, esters and derivatives or mixtures.
Water rinsing of surfaces cleaned with these solvents is difficult because of their inherent lower surface tension. Furthermore, these non-halogenated solvents tend to leave a very thin organic film, after rinsing and drying, adsorbed on the surfaces which negatively interferes in many cases with the next step in a multi-step surface preparation such as etching, plating, painting or thin film coatings by vacuum deposition.
Several plain water ultrasonic and spray rinse steps, following a cleaning step with either water-immiscible or water-emulsifiable or dispersable hydrocarbon non-halogenated solvent cleaners at various temperatures, failed to completely remove the undesirable residue of the organic solvents in the relatively short time which is demanded by typical production requirements. The incomplete removal of the water-immiscible non-halogenated solvent film therefore renders many metallic and non-metallic surfaces, undesirably, water repellant or hydrophobic.
Subsequent processes such as etching, plating, coating, vacuum vapor deposition or painting require water break-free or hydrophilic and rust-free surfaces to produce good results. Otherwise, the surface may suffer, for example, differential etching or coat adhesion problems respectively. Furthermore, a partially hydrophobic surface tends to dewet the rinse water leaving water droplets on the surface (water brake) which may dry in place leaving residual marks on drying. Moreover, the unremoved residuals of hydrocarbons or non-halogenated solvent may contain some of the original surface contaminants. On the other hand, a water break-free surface drains the rinse water faster and requires less energy and time to dry.
For example, metallic and non-metallic substrates which were first treated with a water immiscible (or partially water emulsifiable), heated, hydrocarbon base or non-halogenated solvent concentrate, by immersion in ultrasonically cavitated bath or which were submerged sprayed or simply dipped in with vertical or horizontal oscillation or rotation followed by rinsing with water, or a water diluted emulsion of the same hydrocarbon or non-halogenated solvent, ultrasonically cavitated, or sprayed or submerged sprayed followed by similarly agitated multi water rinses, failed to produce surfaces which are entirely free from the hydrophobic solvent residues. These residues may produce an undesirable odor of the natural hydrocarbons (terpenes) or non-halogenated or petroleum hydrocarbon solvent or included additives; or may interfere with the next step in a manufacturing operation process as aforementioned. Furthermore, the residual hydrocarbon or non-halogenated solvent with low flash point may create a fire-hazard if enough accumulates in the drying step which commonly uses recycled heated air. Air or inert gas drying techniques of those solvents require expensive and complex safeguards against fire hazard and to minimize their vapor release to the environment.
Flash rusting of ferrous metals was less problematic on using the CFC's and halogenated solvents in their cleaning because of the absence of the water element which promotes the formation of surface iron oxides films. Substituting the non-aqueous CFC's or halogenated solvents for cleaning (vapor degreasing) with aqueous cleaning or treatment and hot deionized water rinsing created unacceptable severe flash rusting problems, particularly in the presence of ultrasonic agitation which is needed and required for precision cleaning processes. Furthermore, drying of wet surfaces with hot air intensified the problem. Flash rusting of components made with certain precision, cause catastrophic performance failures in mechanical components such as the auto and aviation fuel injectors, and miniature ball bearings in the disk drive industry. Also, for the precision tooling surfaces that to be modified for better performance and less wear, by coating their surfaces with a thin film of titanium or zirconium nitride, the presence of surface oxides can be detrimental and causes coating adhesion failures and results in changing unevenly the precision tolerances of the tools.
It is therefore highly desirable to provide an improved process and aqueous composition for the cleaning and drying of metallic and non-metallic surfaces which overcomes the above-noted problems resulting from the incomplete removal of the hydrocarbon or non-halogenated solvent. It is also highly desirable to provide other means for ultrasonic aqueous cleaning, ultrasonic deionized water rinsing and air drying of ferrous metal surfaces and components thereof which overcomes the above noted problems and prevents flash rusting during and throughout the entire process and also fulfills the requirements for subsequent treatment steps such as heat treat and thin film coatings deposition.